Scheduling of Irrigation

1. SCHEDULING OF IRRIGATION
 Water management is the planned use of water for better
utilization in agriculture. It includes irrigation (the application of
water to soil or crop or crop plants to assist crop production) and
drainage (removal of excess surface or ground water from land)
by means of surface or sub- surface drains.
 The soil needs the application of water to remove stress
conditions, release nutrients in the soil solution for absorption by
plants, leach or wash out injurious salts from the soil, prepare
land for raising crops and maintain the temperature and
humidity of the soil, maintain micro – climate and the activity of
soil microbes at the optimum level.
 On the other hand excess water needs removal for the normal
aeration and functioning of roots and shoots of the plants except
of aquatic or semi aquatic crops.

2. IRRIGATION
For successful crop production, plants must be supplied with
water as required by them. The water requirement of crops is
that quantity of water required by the crops is that quantity of
water required by the crops with in a given period of time for
their maturity and it included losses due to evaporation plus the
unavoidable losses during the application of water and water
required foe special operations such as land preparation,
puddling and leaching. This water requirement of crops is
partially met by rain or ground water which are very often not
in conformity with the requirement of the crops at different
stages of their life span. Rains do not occur throughout the year
in all cultivable fields and their intensity, duration and
distribution also differ. A very high ground water table is not
always desirable. In such areas, sub surface drainage is needed
for various reasons.

3. Cont……
The application of water is found to be essential for maintaining the
optimum soil moisture balance suitable for the crop variety, its
cultural practices and for other operations such as application of
fertilizers and pesticides, for grain maturity and for case of
harvesting.
The entire volume of water used for irrigation does not meet the
purpose of irrigation as a considerable part is lost in conveyance and
by deep percolation and seepage. Only a percentage serves the
purpose in practice. This is termed irrigation efficiency (the ratio
expresses in percentage of water stored in the root zone depth of the
soil to the water delivered in the field from the farm supply source.)
effective irrigation is the controlled and uniform application of water
to crop land in the required amount at the required time, with
minimum cost to produce optimum yields without wastage of water
and any adverse effect on the soil the form of soil salinity and water
logging problems.

4. SCHEDULING IRRIGATION
•For scheduling irrigation due consideration should be given to
the soil condition, crop variety, type of culture, growth stage of
the crop and atmospheric condition.
•The moisture content in the root zone of soil is determine by
using tensiometers, gypsum block etc.
•They are not always applicable for practical use in the farms.
The use of indicator plants which shows system of wilting earlier
than the plants growing in the field, tissue testing, crop logging
and soil moisture determination are also difficult from farmer
plant of view.
•All these need standardization with respect to soil, season, crop
variety and cultural practices.

5. Cont…..
•Practical experience is essential for scheduling irrigation. For
example wetland rice needs irrigation when the soil surface shows
hair like cracks or even before.
•Once the crack deepens the objective of puddling is defeated as the
cracks make the impervious layers more porous.
•Well fertilized soils, light soils dense leafy, shallow rooted crops and
crop with underground storage tissues require light but frequent
irrigation.
•Deep rooted crop in heavy soils require heavy irrigation with wide
intervals. Heavy soils with shallow rooted crops require light but
frequent irrigation.

6. Cont…..
Further, light but frequent irrigation helps to establish seedlings,
endure moderate vagaries of weather including light showers or
high wind velocity that prevails immediately after irrigation.
The depth of irrigation may be increased with progress of crop
growth up to a certain limit.
Light irrigation at wider intervals helps in uniform and early
ripening of crops. Shallow but repeated irrigation reduces the
injurious effects of salts.

7. Time
Irrigation should be scheduled when the soil temperature is
moderate.
There is greater loss of water through evaporation if irrigation is
applied on hot soil.
The activities of roots make collapse when a sudden drop in soil
temperature or the presence of warm water that receives heat
from the soil. Irrigation on cold soil may injure some crops.
Moreover, during cold period the evaporation rate is less and
water use efficiency is reduced.
Therefore, in hotter season it is better to irrigate the field late
afternoon or at night so that plant and the soil get sufficient time
to absorb water before dry weather prevails the next day.

8. Cont……
If irrigation is extremely necessary during very cold season, then it
should apply during morning hours when the soil starts warming up.
First irrigation to a grown up crop should not be given when it is too
windy as it may result in lodging particularly when the flood method of
irrigation is adopted.
For the furrow method, the first irrigation should be as little water as
possible to stabilize the soil in the ridge.
Frequent irrigation increases application loss and cost but it helps to
increase use efficiency of fertilizer and other inputs.
However, how much water should be applied in each irrigation depends
on the need on the crop for water, the availability of water for
irrigation, the capacity of the root zone soil to store water, the season of
raising the crop, the cultural practices and anticipated rainfall.

9. Cont….
Growing crops use water continuously but the rate of use varies
with the crop grown, the age of the crop, the temperature,
atmospheric condition, special treatment to the crop (use of anti-
transpirents and growth modifiers) and the moisture status of the
soil.
It is not desirable or possible to supply water uniformly
throughout the life span of the crop. There are certain critical
periods of water requirement for each crop. If the crop experiences
stress condition during these periods there is drastic reduction in
yield. These periods are mostly specific.
Therefore irrigation should be applied/ schedule around such
critical stages of water requirement of the crop provided there is
no other source to recharge the root zone with the moisture.

10. CROP CRITICAL STAGES
Rice Tillering initiation, flower premordia and
flowering
Wheat Crown root initiation (CRI), milk
Maize Silking, cob developing
Sorghum Seedling, flowering
Red gram Flower initiation, pod filling
Peas Start of flowering, pod formation
Linseed Pre flowering, capsule development
Sunflower Flowering, grain filling
Different growth stages of different crops have been recognized
as critical stages of water requirement are as follows

11. At each irrigation a volume of water sufficient to supply
the seeds of the crop for a period varying from a few days to
several weeks is stored in the unsaturated soil in the form of
available soil water.
Irrigation practices, comprise of three
interlinked components:
•The quantity of water at each irrigation ( normally 5-10 cm)
•The interval between to irrigations (normally 10-20 days)
•Total number of irrigations in the life span of a crop (1 to 50 or
more)